Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages
Filter by Categories
Case Report
Clinical research study
Current Issue
Editorial Board
Literature Review
Narrative review
Original Article
Research Article
Review Article
Short Report
Surgical techniques
Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages
Filter by Categories
Case Report
Clinical research study
Current Issue
Editorial Board
Literature Review
Narrative review
Original Article
Research Article
Review Article
Short Report
Surgical techniques
View/Download PDF

Translate this page into:

43 (); 93-100
doi:
10.1016/j.jor.2023.06.009

Subsidence analysis of a cementless short stem THA using EBRA-FCA - A seven-year prospective multicentre study

, , , , , , ,
a UKSH Campus Lübeck, Klinik für Orthopädie und Unfallchirurgie Sektion Orthopädie, Ratzeburger Allee, Lübeck, Germany
b Ordensklinikum Linz, Krankenhaus der Barmherzigen Schwestern Linz GmbH, Seilerstätte, Linz, Austria
c Klinikum Dahme-Spreewald GmbH, Lübben (Spreewald), Germany
d Helios Klinik Köthen, Hallesche Straße, Köthen (Anhalt), Germany
e Kreiskrankenhaus Stollberg GmbH, Jahnsdorfer Straße Stollberg, Stollberg, Germany
f Praxis für Orthopädie und Unfallchirurgie, Friedrichstraße, Erkner, Germany
g Christophorus Kliniken Coesfeld, Südring 41, 48653, Coesfeld, Germany

∗Corresponding author: Jan C. Schagemann. jancarl.schagemann@christophorus-kliniken.de

Received: , Accepted: ,
Professor P K Surendran Memorial Education Foundation
Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Abstract

Metaphyseal fixation of short stem THA allows for minimally invasive surgery, less bone removal, improved bone load transfer and reduced stress shielding. Short stems facilitate the anatomic restoration i.a. of leg length, femoroacetabular offset, and center of rotation. However, metaphyseal fixation might cause impaired primary and/or secondary stability resulting in an inherent tendency for early axial migration and aseptic loosening eventually. The objective of this study was to investigate the long-term outcome and migration pattern of a calcar-guided short stem.

In a prospective multicenter study, 213 patients (224 THAs) were enrolled. Patients were followed for up to 84 months postoperatively. Clinical outcome was assessed using the Harris Hip Score and the VAS for pain and satisfaction. Standardized and calibrated radiographs were screened i.a. for stress shielding and loosening. Einzel-Bild-Roentgen-Analyse – femoral component analysis (EBRA-FCA) was used to detect longitudinal subsidence.

At 7 year follow-up, n = 139/224 cases were available for analysis. All clinical parameters improved significantly (p < 0.001) and improvement persisted. There were no radiographic changes indicating stress shielding. EBRA-FCA revealed a mean subsidence of −1.44 mm followed by a stabilization. Weight >80 kg (p = 0.115), BMI <30 kg/m2 (p = 0.282), male gender (p = 0.246), and age <65 years (p = 0.304) seemed to be associated with a higher risk for migration. The cumulative revision rate was 2.23%. Revisions due to stem migration (0.89%) occurred early (mean time between index surgery and revision: 3.3 months).

If at all, there appears to be a pronounced initial subsidence, which stabilizes thereafter. Stem migration was rarely a compelling reason for failure or revision. Demographics do not seem to have a significant effect on migration pattern. The absence of radioluce lines, resorption or hypertrophy of the proximal femora support the hypothesis of a reduced stress shielding for metaphyseal anchoring short stems.

Keywords

Total hip arthroplasty
Hip prosthesis
Short stem
Metaphyseal fixation
Stress shielding
Migration
Bone preservation
Subsidence
EBRA-FCA
1

1 Introduction

There is an ongoing trend towards the implantation of cementless short stem total hip arthroplasty (THA).1–3 Femoral implants with various short stem designs are labeled to preserve proximal femoral bone stock.4 The underlying rationale is that metaphyseal fixation allows for minimally invasive (round the corner) implantation together with less bone removal and reduced stress shielding.5,6 Particularly younger patients could benefit as they are likely to undergo revision surgery.

When comparing short and conventional straight stems, short stems were shown to provide equivalent mid-term results together with fewer intraoperative complications7 and high survival rates.8 To achieve this, it seems to be crucial to re-establish the true anatomy including leg length, femoroacetabular offset, center of rotation, and caput-collum-diaphyseal (CCD) angle.9,10 The design and the shape of the optimys short stem (Mathys Ltd. Bettlach/CH) perfectly fits the geometry of the proximal femur and follows the principles of neck-preserving, calcar guided metaphyseal fixation. Moreover, individual implantation of the stem in either varus or valgus hips allows for reconstruction of the offset and CCD angle thereby accomplishing soft tissue balancing.9,11–13

Metaphyseal fixation, however, might cause impaired primary and/or secondary stability resulting in migration.4,14,15 Implant migration is considered to be a major cause for implant failure due to aseptic loosening.14,16 There is evidence that various short stems hold an inherent tendency for early axial migration.12,14,17–20 At least for conventional stems, early postoperative migration might be an indication of subsequent aseptic loosening and failure eventually.21,22 Whether this applies to short stems, remains uncertain as long-term follow-up studies are still lacking.12,14,21,23

Therefore, the objective of the present prospective multicentre study was to track our previous short-term follow-up publication20 and to outline the clinical outcome of the optimys short stem together with specific migration pattern and relating risk factors for up to 7 years follow-up. To achieve this goal, the cohort was analyzed using the Harris Hip Score (HHS), the visual analogue scale (VAS) for pain and satisfaction, and digital series of standardized and calibrated anteroposterior radiographs for Einzel-Bild-Roentgen-Analyse – femoral component analysis (EBRA-FCA).

2

2 Methods

2.1

2.1 Study design

A prospective multicenter study involving six European orthopaedic centers and eight experienced senior orthopaedic surgeons was conducted. Patients who received primary THA using the optimys short stem were enrolled between 2012 and 2013. Prosthetic components such as cups, liners and ball heads were unrestricted. Exclusion criteria for participation were revision surgery, periprosthetic joint infections, severe developmental dysplasia of the hip (DDH), malignant tumors, a body mass index >35, or an American Society of Anesthesiologists (ASA) score of >3.

2.2

2.2 Follow-up

Patients were examined clinically and radiographically at 6–12 weeks, at 1, 2, 5 and 7 years postoperatively. Clinical outcome measures included the Harris Hips Score (HHS) and the visual analogue scale (VAS) for pain both under load and rest (0: no pain; 10: worst pain) and for patient satisfaction (0: no satisfaction; 10: greatest satisfaction). Standardized anteroposterior radiographs (at 20° of hip internal rotation) and Lauenstein's projections using reference spheres were taken. For constant and systematic imaging, the institutional radiology departments were accordingly instructed. Radiological assessment including stem migration, resorption of femoral bone, resorption of calcar, interface radiolucent lines, or hypertrophy of femoral bone was visually accomplished by specifically trained readers in an independent manner.

2.3

2.3 Einzel-Bild-Roentgen-Analyse – femoral component analysis

One specifically trained yet independent reader conducted the longitudinal/transversal subsidence analysis of the femoral component (stem) using the EBRA-FCA software (University of Innsbruck/AUT).24 Digital serial anteroposterior radiographs of the pelvis or hip were calibrated by head diameter. FCA landmarks were as defined by the originator: at least 3 on head contour, 4 defining the stem axis, 2 on the greater and lesser trochanter, 1 on the prosthetic shoulder, and 8 on the femoral contour.

2.4

2.4 Statistics

Data acquisition was using Microsoft Excel. Descriptive data analysis involved means and standard deviation (SD), and median, range and 95% confidence interval (CI) where applicable. The Wilcoxon signed-rank test was used to assess differences between preoperative and follow-up examination values. Level of significance was set at α < 0.05. All analysis were performed using SAS Enterprise Guide (Version 9.4; SAS Institute Inc., Cary, NC, USA) and R (Version 4.2.1; RStudio, Version 2022.7.0.548). In order to unify the differing time-points of the EBRA-measurements (such for generating box-plots or calculating interval-based descriptive statistics) all time-points were reprocessed to yield clear-cut defined monthly periods. In order to determine whether substantial migration occurred in the time-course of follow-up starting with the baseline assessment, the basic regression analysis based upon so called random effects-models, treating each patient as a block variable, was performed. This assured that (i) the estimation of the effects is optimally weighted based upon the available patient and time-point data, and more important (ii) the correlation within the time-profiles (i.e. patients) was accounted for thereby minimizing the risk of ‘inflating’ the p-values with standard errors. The time-slope was modelled using a polynomial fit based on a linear term along with a quadratic and a cubic term. For the sake of simplicity line-plots with all estimated weighted average time-courses with their 95%CI-envelopes presented. The LOESS procedure, a nonparametric method for estimating the regression line, was applied as a complement for visual display of the time-course. This approach allowed for great flexibility because no assumptions about the parametric form of the regression surface are needed. The aim of this additional analysis was to summarize the estimated average time-course of subsidence over time to elucidate the time-pattern.

Ethical statement

All procedures involving human participants compiled with the ethical standards of the institutional and/or national research committee as well as with the 1964 Declaration of Helsinki and its later amendments. The ethics committee of the University of Lübeck/DE (AZ 12-112) and the Freiburg Ethics Commission International (feki cde 012/280) approved the study protocol. The Bundesamt für Strahlenschutz authorized the radiographic follow-up examination of the participants (AZ Z5-22462/2-2016-111). Participation was voluntary. Informed consent was obtained.

3

3 Results

3.1

3.1 Demographics

Between July 2012 and September 2013, n = 213 patients (224 THAs) were enrolled for primary (67%) or secondary osteoarthritis (OA; 17.9%), avascular necrosis of the femoral head (AVN; 8.0%), mild to moderate DDH (6.3%), femoral neck fractures (0.4%), or rheumatoid arthritis (RA; 0.4%; Fig. 1). The Charnley score was as follows: A: unilateral hip disease 56.7%, B: bilateral hip disease, otherwise physically fit 38.4%, C: uni- or bilateral hip disease with other factors affecting the function of walking 4.9% (BB: presence of two artificial joints 0%). Each of the six orthopaedic centers enrolled between 13.4 and 21.4% of the participants.

Flow chart of study population selection. For final follow-up at 7 years n = 139 cases of THA with the optimys stem implanted were available (n = 115 EBRA-FCA).
Fig. 1 Flow chart of study population selection. For final follow-up at 7 years n = 139 cases of THA with the optimys stem implanted were available (n = 115 EBRA-FCA).

At final follow-up at 7 years, n = 2 bilateral patients and n = 111 unilateral patients (total n = 115 cases; gender female n = 65, male n = 50, side left: n = 54, right: n = 61, head size 36: 40.9%, 32: 53.9%, 28: 5.2%) were available for EBRA-FCA (Fig. 1). The following demographics and analysis refers to this cohort: The median age was 60.3 (range: 35 to 80). Females were of older age (median: 62.7, range: 35 to 80; males: median: 56.8, range: 41 to 77), the difference being statistically significant (p = 0.016). Table 1 depicts the specific demographics. The median follow-up time for EBRA-FCA was 84 months. The 25% percentile was 83 months, thus more than 75% had a follow-up of longer than 7 years. There was no gender difference with regard to follow-up length (p = 0.871). Details concerning approach, mean duration of surgery or stem design can be reviewed in our previous follow-up study.20

Table 1 Demographics.
Statistics Age Height Weight BMI
Female n 65 65 65 65
Mean (SD) 62.3 (8.32) 165.2 (6.06) 75.9 (13.59) 27.8 (4.56)
95% CI 60.3, 64.4 163.7, 166.7 72.5, 79.3 26.7, 28.9
Median 62.7 165.0 75.0 27.7
Range 35 to 80 152 to 176 51 to 106 19 to 39
Male n 50 50 50 50
Mean (SD) 58.8 (9.11) 178.4 (8.12) 91.5 (14.77) 28.7 (3.47)
95% CI 56.2, 61.4 176.1, 180.7 87.3, 95.7 27.7, 29.6
Median 56.8 178.0 88.5 28.4
Range 41 to 77 163 to 196 63 to 140 21 to 37
Total n 115 115 115 115
Mean (SD) 60.8 (8.81) 170.9 (9.60) 82.7 (16.05) 28.2 (4.12)
95% CI 59.2, 62.4 169.2, 172.7 79.7, 85.6 27.4, 28.9
Median 60.3 170.0 83.0 28.3
Range 35 to 80 152 to 196 51 to 140 19 to 39
3.2

3.2 Clinical outcome

We published clinical data at 24 months follow-up previously.20 Briefly, all clinical parameters including the HHS, the VAS for pain under load and rest, and for satisfaction improved significantly (p < 0.001) over the first 6–12 weeks, and this improvement lasted for up to 24 months. At 7-year follow-up, the significant improvement persisted with a mean HHS of 95.5 ± 8.4 SD compared to preoperative values (mean 50.8 ± 12.1 SD), and values at 6–12 weeks follow-up (mean 87.7 ± 13.7 SD) and at 24 months follow-up (mean 95.3 ± 6.7 SD). Improvement was seen for pain under load with a mean VAS of 0.6 ± 1.3 SD (preoperative: mean 7.7 ± 1.5 SD) and for pain at rest with a mean VAS of 0.2 ± 0.7 SD (preoperative: mean 5.4 ± 2.6 SD), and for satisfaction with a mean VAS of 9.6 ± 0.8 SD (preoperative: mean 2.3 ± 2.1 SD) also. No complications since last follow-up at 5 years were detected or documented.

3.3

3.3 Radiographic outcome

At 7-year follow-up, radiographic changes indicating stress shielding such as osteolysis, hypertrophy and/or resorption of femoral bone, resorption of calcar, or interface radiolucent lines were not detected (Table 2). The occurrence of heterotopic ossifications was rare and remained almost constant.

Table 2 Radiographic analysis.
6–12 weeks n = 199 (%) 12 months n = 198 (%) 24 months n = 191 (%) 5 years n = 171 (%) 7 years n = 139 (%)
osteolysis of femoral bone 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0)
resorption of femoral bone 0 (0.0) 0 (0.0) 1 (0.5) 0 (0.0) 0 (0.0)
resorption of calcar 4 (2.0) 3 (1.5) 2 (1.0) 2 (1.2) 0 (0.0)
interface radioluce lines 0 (0.0) 0 (0.0) 1 (0.5) 0 (0.0) 0 (0.0)
hypertrophy of femoral bone 1 (0.5) 3 (1.5) 1 (0.5) 0 (0.0) 0 (0.0)
heterotopic ossification Brooker I 2 (1.0) 3 (1.5) 4 (2.1) 4 (2.3) 4 (2.9)
Brooker II 1 (0.5) 3 (1.5) 1 (0.5) 2 (1.2) 1 (0.7)
Brooker III 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0)
3.4

3.4 EBRA-FCA

At final follow-up at 7 years, n = 115 cases with n = 411 images were available for the EBRA-measurements, i.e. 3.6 images per case on the average (range: 2–7). Table 3 depicts the results of the whole image series as the distribution of subsidence was stratified by time-intervals (unit = image).

Table 3 Subsidence.
Subsidence [mm] by Time Interval (unit = image)
Month N Obs Mean Stdev. Median 25% Pctl 75% Pctl Low CL Up. CL Min Max
0 115 0.00 0.00 0.00 0.00 0.00 . . 0.00 0.00
12 19 −0.84 1.22 −0.34 −1.50 0.01 −1.43 −0.26 −4.45 0.62
24 69 −0.82 1.31 −0.51 −1.12 −0.06 −1.13 −0.50 −6.63 0.93
60 87 −1.14 1.96 −0.80 −1.85 −0.08 −1.56 −0.72 −11.35 3.00
84 111 −1.31 2.36 −0.96 −2.38 0.26 −1.76 −0.87 −11.50 4.60

However, the average subsidence at 7-year follow-up was −1.44 mm ± 2.46 SD (females: mean: −1.16 mm ± 2.04 SD; males: mean: −1.8 mm ± 2.9 SD; p = 0.246). The median was −1.22 mm, which is slightly lower than the mean hence reflecting either a skewed distribution or a substantial fraction of outliers. The 95% CI upper limit does exceed −1.00 mm, considered as the inherent measurement error of the EBRA method. Note that for this assessment only the last non-missing control was used. Episodic exceedance prior to the last control was not considered. There were not significant differences across the clinics (p = 0.391), or for head size (p = 0.462). Worth noting, however, was that medians for head sizes 32 and 36 indicated lower subsidence than compared to 28. The opposite pattern was seen in the last analysis (data not shown). Moreover, EBRA-FCA revealed that younger patients had a higher risk for subsidence, although this was not significant either (>65 years: mean: −1.24 mm ± 2.37 SD; <65 years: mean: −1.52 mm ± 2.51; p = 0.304).

When stratified for weight classes (</> 80 kg) or BMI (</> 30 kg/m2) data were inconclusive: weight >80 kg was associated with an increased mean subsidence of −1.6 mm ± 2.46 SD vs. −1.25 mm ± 2.47 SD in the <80 kg class. In contrast, BMI >30 kg/m2 was associated with a lower mean subsidence of −1.39 mm ± 1.64 SD vs. −1.45 mm ± 2.74 SD in the >30 kg/m2 class. Differences, however, were not statistically significant (p = 0.115 respectively p = 0.282; Fig. 2).

Distribution of subsidence Left: Distribution of subsidence [mm] at last follow-up stratified by weight classes (top). Scatterplot of subsidence at last follow-up vs. weight (bottom). Right: Distribution of subsidence [mm] at last follow-up stratified by BMI classes (top). Scatterplot of subsidence at last follow-up vs. BMI (bottom).
Fig. 2 Distribution of subsidence Left: Distribution of subsidence [mm] at last follow-up stratified by weight classes (top). Scatterplot of subsidence at last follow-up vs. weight (bottom). Right: Distribution of subsidence [mm] at last follow-up stratified by BMI classes (top). Scatterplot of subsidence at last follow-up vs. BMI (bottom).
3.4.1

3.4.1 EBRA-FCA: Exceedance

Any value above a defined threshold such as a cut-off of 1 mm was termed exceedance, since the accuracy of the method lies between ±1 mm.24 Exceedance was hence a suitable test for migration to examine in how many cases the cut of 1 mm was exceeded. The fraction of cases above this cut-off could then be used as a summary measurement for migration. The lower this fraction is, the less subsidence was observable (subsidence threshold > -1 mm: 50.43%, >-1.5 mm: 44.35%, >-2.0 mm: 30.43%, >-5.0 mm: 4.35%). This means that in 49.57% of the cases no migration was detected. In 69.57% of the cases, migration was less than −2.0 mm, and in 95.65% of the cases less than −5 mm. Overall n = 5 cases had a subsidence > -5 mm (mean: 9.5 mm, range: 7.73–11.5 mm) at final follow-up. It is worth mentioning, that this substantial subsidence did not lead to a failure in terms of stem revision as endpoint or any revision as endpoint.

In the following, we focused on the time-profile of the patients with migration amounting to −2 mm or more at any time-point at the last non-missing control (Fig. 3 left). Note that for this assessment only the last non-missing control was used. Episodic exceedance prior to the last control was not considered. Except for n = 5 outliers with a subsidence of > -5 mm at last follow-up, there was a trend for initial migration followed by a stabilization.

Stem migration over time Left: Stem migration over time for patients with subsidence exceeding −2.0 mm. Right: Migration values over time including estimated regression line. For graphical purposes the estimated regression line was based upon a categorical model treating each month as an indicator variable to achieve a smooth fit.
Fig. 3 Stem migration over time Left: Stem migration over time for patients with subsidence exceeding −2.0 mm. Right: Migration values over time including estimated regression line. For graphical purposes the estimated regression line was based upon a categorical model treating each month as an indicator variable to achieve a smooth fit.
3.5

3.5 Quantitative assessment of migration

The random effects model (polynomial fit) revealed a significant decrease of subsidence over time (linear term p = 0.0005). However, the decrease flattened out as shown by the quadratic term in the model (monthsq p = 0.0387). In turn, the cubic term was not significant (monthsc p = 0.1012). The subsidence appeared to be rather substantial, the 95% envelope of the regression curve does exclude −1 mm, hence is statistically significant different from the −1 mm line (Fig. 3 right). The Loess procedure showed a pronounced initial subsidence, which stabilizes thereafter (Fig. 4).

Loes fitting The Loess fitting with individual time-point data (top) and with grouped interval time-point data (bottom) demonstrates a pronounced initial subsidence, which stabilizes thereafter.
Fig. 4 Loes fitting The Loess fitting with individual time-point data (top) and with grouped interval time-point data (bottom) demonstrates a pronounced initial subsidence, which stabilizes thereafter.
3.6

3.6 Survival rate

At 7-year follow-up, the survival rate was 97.77%, n = 5 cases had to undergo revision either due to aseptic loosening (n = 1; changed component: cup; time until revision: 49.9 months), septic loosening (n = 1; changed components: stem and head; time until revision: 3.2 months), periprosthetic fracture (n = 1; all component changed; time until revision: 6.6 months), or stem migration (n = 2; changed components: case 1: stem, case 2: stem, head, inlay). Revisions due to stem migration occurred early with a mean time of 3.3 months (range: 2.8–3.8 months) from index surgery until revision. Fig. 5 depicts the survival rates for stem revision as endpoint and for any revision as endpoint.

Survival rate Survival rates for stem revision as endpoint (left) and for any revision as endpoint (right).
Fig. 5 Survival rate Survival rates for stem revision as endpoint (left) and for any revision as endpoint (right).
4

4 Discussion

In order to prove the superiority of a new stem design, long-term studies and registry data are indispensable.8 Most recently, Kutzner et al. published a prospective mid-term multicenter study of the calcar-guided short stem optimys following 879 THAs for up to 6 years.25 The authors described an excellent outcome as for PROMs and a survival rate of 98.4% for any cause of stem revision together with a low complication rate. Reasons for early stem revision were either aseptic loosening or periprosthetic fractures. These findings correspond to our results following 224 THAs using the optimys stem for more than 7 years. We could demonstrate excellent PROMs and a low complication rate also. Heterotopic ossifications were rarely seen - a general observation for minimally invasive approaches and bone sparing implantation.26 Stem revision as endpoint only occurred in a few cases for the same reasons and very early. In these cases, severe undersizing was most likely causal.12,20,25 In order to avoid this technical error, optimys users generally “recommend perioperative radiological controls”.13,27

However, the degree of initial subsidence is suspected to be one of the major reasons for revision and as an endpoint at least for conventional stem designs.21,22 Radiostereometric analysis (RSA) and EBRA-FCA were shown to be suitable tools to assess wear and migration of the femoral component after THA.24,28 Using the latter technique, Kutzner et al. published promising mid-term results of the calcar-guided short stem optimys following 162 patients for up to 5 years.12 Mean axial subsidence was described to be −1.5 mm. In most cases a secondary setting could be observed. In a few cases ongoing subsidence could be detected with undersizing as the underlying cause. Subsidence, however, was not found to be a reason for stem revision in either group. Therefore, the authors concluded a different migration pattern together with a two-stage settlement of this particular stem compared to conventional stem designs without being relevant for survivorship.12

This is consistent with data published by Djebara et al.29 The authors investigated the bone mineral density (BMD) using dual-energy x-ray absorptiometry (DEXA) after two different short stem THAs (Vitae vs. optimys). A significant decrease of BMD could be observed in Gruen zones 7, 2 and 6 in the Vitae group, and in zone 2 in the optimys group with the latter group demonstrating significantly higher BMD at the calcar (zones 6 and 7) together with an increased femoral offset at 4 year follow-up. Hochreiter et al. showed that BMD increased mainly in the lateral region (Gruen zones 2 and 3) and in the distal-medial region (Gruen zone 5), suggestive of lateral loading of the optimys stem.30 Most caput-collum-diaphyseal angles were steady after surgery, especially in varus hips. Short stems minimized stress shielding and periprosthetic bone loss without compromising primary stability. Yan et al. implemented a comparative finite element analysis (FEA) and demonstrated that both short and standard THA caused unloading of the proximal femur.5 But the metaphyseal anchoring short stems showed a favorable pattern in terms of a lower reduction proximally and improved metaphyseal loading, while pattern of conventional stems was vice versa. The authors concluded a reduced stress shielding proximally for metaphyseal anchoring short stems. Thus, the hypothesis that a calcar guided short stem with a meta(dia)physeal fixation results in a more physiological load transfer that prevents stress shielding makes perfect sense from a biomechanical prospective (i.e. Wolff's Law). And our results support this hypothesis: changes of femoral bone indicative of stress shielding resulting in aseptic loosening eventually were not detected long-term. In conclusion, different short stems promote different yet beneficial load distributions. But bone remodeling appears to continue beyond 1 year postoperative.

Our EBRA-FCA results on the optimys stem for up to more than 7 years match the observations by Kutzner et al.12 Mean subsidence was −1.44 mm. Initial migration was followed by settlement by all means. Stem revision as endpoint occurred in a few cases very early. In contrast, ongoing migration was not found to be a compelling reason for stem revision. This corresponds to EBRA of various other short stem designs ranging from −0.24 mm (MiniHip, Corin, Cirencester, UK) and −0.7 mm (Metha, B. Braun, Melsungen, Germany) to −1.1 mm (Fitmore, Zimmer, Warsaw, USA) and −2.04 mm (Nanos, Smith & Nephew, Memphis, USA) within the first 2 years of follow-up.5,31–33 Again, subsequent settlement was detected. And as summarized, short stem designs seem to have early migration within the first months postoperation in common.12

Nonetheless, risk factors for stem (optimys) specific failures such as migration naturally exist23: Clinically seen, age and higher BMI as well as Dorr B and C types of proximal femora were shown to be potentially associated with a higher risk for stem revision, whereas gender had no effect.25 From a migration prospective, male gender, heavy weight, and extensive valgus positioning of the stem significantly increased the risk for migration, whereas Dorr A and B subtypes were not significantly different.12 In our patient sample, subsidence was associated with male gender and heavy weight, yet with younger age and low BMI also. Higher load and activity could be a reason for the age-related effect, and osteoporosis for the latter34,35? This is worth discussing, because when looking at the EPRD, overall 41.7% of the patients who underwent THA were age 75 years and older. 60.3% were females with a mean age of 73 years.36 And there is evidence that patients age 75 years and older benefit from a cemented stem. Based on this data, a high rate of cemented stems was expected, however, the data was different. The rate of uncemented stems in cases of primary THA was 76.9% and almost constant. And the prevalence of short stems doubles from 2015 to 12.0%. This raises the question of whether we tend to disregard evidence, or if age-related effects, which are neither significant in our population nor in the population of Kutzner et al.,25 are not conditioned to short stems?

However, the success of the optimys stem is certainly multifactorial: Besides skills, approaches, or postoperative protocols, individual stem positioning ensures soft tissue balancing and reconstruction of the true anatomy in fact. This what so ever depends on the “correct level of osteotomy”, which requires “a considerable experience”.11 Extensive valgus alignment is demanding and relies on accurate contact to the lateral cortex.13,37 On the other hand, the optional varus and valgus alignment as well as three-point metaphyseal fixation or metadiaphyseal fit-and-fill positioning sums up to the stem's versatility.38,39 When speaking of bone preservation, the articulating counterpart(s) need attention. EPRD data reveals that in a majority of modular cups (88.9%), the rate of dual mobility increased (1.9%), and the rate of mononbloc cups decreased (9.0%). Literature available to date, however, indicates that the 3rd generation of cementless isoelastic monobloc cups made of highly cross-linked polyethylene (HXLPE; infused with vitamin E) promote excellent biomechanical properties e.g. reducing equatorial stress together with a low revision, wear and migration rate for up to 5 years of follow-up.40–43 And the combination of an isoelastic cup and a short stem might be favorable in terms of BMD regulation.44

The present study has several limitations: Although our previous 2-year follow-up of the study's population was amended by the addition of EBRA-FCA for up to 7 years of follow-up, subgroup analysis of different Dorr classifications and varus/valgus alignment were not performed. BMD analysis comparable to EBRA could have shed some light on the influence of osteoporosis on pronounced migration. Drop outs over time decreased the strength of the prospective evaluation.

4.1

4.1 Conclusions

The optimys stem is safe and versatile, and provides excellent clinical outcome and low complication rates. Male gender and heavy weight are potentially associated with a higher risk for migration and/or revision eventually. Long-term studies are necessary for a final assessment. The higher rate of migration in our low BMI group might indicate impaired bone quality. BMD analysis could be complementary to EBRA. The impact of age remains unclear. Subgroup analysis and registry data of the age-related effects on short stems are awaited.

Funding

The study group received partial funding for travel expenses (study group meetings), conceptualization, data curation, and statistical advice provided by Mathys Orthopädie GmbH Bochum/DE and Mathys Ltd. Bettlach/CH. There was no other funding, and no personal funding or funding for personnel.

Editing and proof reading

P. Barrier, M.D., Mayo Clinic Rochester, MN, USA.

References

  1. , , . A differentiated view on short stemmed hip arthroplasty - what are the differences in fixation and biomechanics? Z für Orthop Unfallchirurgie. 2019;157(5):548-557.
    [Google Scholar]
  2. , , , , , . Short bone-conserving stems in cementless hip arthroplasty. Journal of Bone and Joint Surgery - American. 2014;96(20):1742-1752.
    [Google Scholar]
  3. , , , , , , . Zementfreie Kurzschaftprothesen in der Hüftendoprothetik: Möglichkeiten und Limits. 2022
    [Google Scholar]
  4. , , , et al . The migration pattern and initial stability of the Optimys short stem in total hip arthroplasty: a prospective 2-year follow-up study of 33 patients with RSA. HIP Int. 2021;31(4):507-515.
    [Google Scholar]
  5. , , , et al . Metaphyseal anchoring short stem hip arthroplasty provides a more physiological load transfer: a comparative finite element analysis study. J Orthop Surg Res. 2020;15(1):498.
    [Google Scholar]
  6. , , , , . Biomechanics of a short stem: in vitro primary stability and stress shielding of a conservative cementless hip stem. J Orthop Res. 2013;31(8):1180-1186.
    [Google Scholar]
  7. , , , , , . A short tapered stem reduces intraoperative complications in primary total hip arthroplasty. Clin Orthop Relat Res. 2012;470(2):450-461.
    [Google Scholar]
  8. , , , , , , . Survival rate of short-stem hip prostheses: a comparative analysis of clinical studies and national arthroplasty registers. J Arthroplasty. 2018;33(6):1800-1805.
    [Google Scholar]
  9. , , , , , . Reconstruction of femoro-acetabular offsets using a short-stem. Int Orthop. 2015;39(7):1269-1275.
    [Google Scholar]
  10. , , , , , , . Effects of the femoral offset and the head size on the safe range of motion in total hip arthroplasty. J Arthroplasty. 2009;24(4):646-651.
    [Google Scholar]
  11. , , . Individualized stem-positioning in calcar-guided short-stem total hip arthroplasty. J Vis Exp. 2018;132
    [Google Scholar]
  12. , , , , , , . Mid-term migration pattern of a calcar-guided short stem: a five-year EBRA-FCA-study. J Orthop Sci. 2020;25(6):1015-1020.
    [Google Scholar]
  13. , , , , , . Outcome of extensive varus and valgus stem alignment in short-stem THA: clinical and radiological analysis using EBRA-FCA. Arch Orthop Trauma Surg. 2017;137(3):431-439.
    [Google Scholar]
  14. , , , , , , . Migration analysis of a metaphyseal-anchored short femoral stem in cementless THA and factors affecting the stem subsidence. BMC Muscoskel Disord. 2019;20(1):604.
    [Google Scholar]
  15. , , , et al . Biomechanics of a calcar loading and a shortened tapered femoral stem: comparative in-vitro testing of primary stability and strain distribution. J Exp Orthop. 2021;8(1):74.
    [Google Scholar]
  16. , . Radiostereometric analysis of early implant migration - a valuable tool to ensure proper introduction of new implants. Acta Orthop. 2012;83(6):551-552.
    [Google Scholar]
  17. , , , , , . Migration characteristics and early clinical results of the NANOS® short-stem hip arthroplasty. Wien Klin Wochenschr. 2015;127(9-10):375-378.
    [Google Scholar]
  18. , , , , , , . Migration pattern of a femoral short-stem prosthesis: a 2-year EBRA-FCA-study. Arch Orthop Trauma Surg. 2014;134(7):1003-1008.
    [Google Scholar]
  19. , , , , , , . One-stage bilateral versus unilateral short-stem total hip arthroplasty: comparison of migration patterns using “Ein-Bild-Roentgen-Analysis Femoral-Component-Analysis.”. Int Orthop. 2017;41(1):61-66.
    [Google Scholar]
  20. , , , et al . Calcar-guided short stems in total hip arthroplasty: a two-year prospective multicentre study. Open Orthop J. 2020;14(1):33-38.
    [Google Scholar]
  21. , , , et al . Early migration predicts aseptic loosening of cementless femoral stems: a long-term study. Clin Orthop Relat Res. 2016;474(7):1697-1706.
    [Google Scholar]
  22. , , , , , , . The prediction of failure of the stem in THR by measurement of early migration using EBRA-FCA. Journal of Bone and Joint Surgery - Series B. 1999;81(2):273-280.
    [Google Scholar]
  23. , , , , , . Mid-term migration analysis of a femoral short-stem prosthesis: a five-year EBRA-FCA-study. HIP Int. 2019;29(2):128-133.
    [Google Scholar]
  24. , , , , , , . Accuracy of EBRA-FCA in the measurement of migration of femoral components of total hip replacement. Journal of Bone and Joint Surgery - Series B. 1999;81(2):266-272.
    [Google Scholar]
  25. , , , , , . Survivorship, complications and patient-reported outcomes in calcar-guided short-stem THA: prospective mid-term multicenter data of the first 879 hips. Arch Orthop Trauma Surg. 2023;143(2):1049-1059.
    [Google Scholar]
  26. , , , et al . Incidence of heterotopic ossification in minimally invasive short-stem tha using the modified anterolateral approach. HIP Int. 2017;27(2):162-168.
    [Google Scholar]
  27. , , , et al . The learning curve in short-stem THA: influence of the surgeon's experience on intraoperative adjustments due to intraoperative radiography. Eur J Orthop Surg Traumatol. 2018;28(2):269-275.
    [Google Scholar]
  28. , , , . EBRA improves the accuracy of radiographic analysis of acetabular cup migration. Acta Orthop Scand. 1998;69(2):119-124.
    [Google Scholar]
  29. , , , , , , . Comparison of periprosthetic bone mineral density between two types of short-stems in total hip arthroplasty with a mean follow-up of 4 years. J Orthop Traumatol: Surgery and Research. 2022;108(1)
    [Google Scholar]
  30. , , , , , . Femoral bone remodeling after short-stem total hip arthroplasty: a prospective densitometric study. Int Orthop. 2020;44(4):753-759.
    [Google Scholar]
  31. , , , , , . Influence of varus/valgus positioning of the Nanos® and Metha® short-stemmed prostheses on stress shielding of metaphyseal bone. Acta Orthop Belg. 2017;83(1):57-66.
    [Google Scholar]
  32. , , , , , . A prospective randomized radiographic and dual-energy X-ray absorptiometric study of migration and bone remodeling after implantation of two modern short-stemmed femoral prostheses. J Orthop Traumatol. 2015;16(3):237-243.
    [Google Scholar]
  33. , , , et al . Primary stability of a short bone-conserving femoral stem. Bone and Joint Journal. 2018;100-B(9):1146-1147.
    [Google Scholar]
  34. , , , , , , . Osteoporosis among fallers without concomitant fracture identified in an emergency department: frequencies and risk factors. Adv Orthop. 2011;2011
    [Google Scholar]
  35. , , , . Clinical relevance of bone remodelling around conventional and conservative (short-stem) total hip arthroplasty implants. HIP Int. 2019;29(1):4-6.
    [Google Scholar]
  36. , , , , , . Jahresbericht 2022: Mit Sicherheit Mehr Qualität. 2022
    [Google Scholar]
  37. , , , . Defining ‘undersizing’ in short-stem total hip arthroplasty: the importance of sufficient contact with the lateral femoral cortex. HIP Int. 2022;32(2):160-165.
    [Google Scholar]
  38. , , , et al . Primary stability of calcar-guided short-stem total hip arthroplasty in the treatment of osteonecrosis of the femoral head: migration analysis using EBRA-FCA. Arch Orthop Trauma Surg. 2020;140(12):2091-2100.
    [Google Scholar]
  39. , , , , , , . Downsizing in total hip arthroplasty. A short stem as a revision implant. Orthopä. 2022;51(3):230-238.
    [Google Scholar]
  40. , , , , . A vitamin E blended highly cross-linked polyethylene acetabular cup results in less wear: 6-year results of a randomized controlled trial in 199 patients. Acta Orthop. 2020;91(6):705-710.
    [Google Scholar]
  41. , , , et al . Oxidation prevention with vitamin e in a HXLPE isoelastic monoblock pressfit cup: preliminary results. 2012:21-31.
    [Google Scholar]
  42. , , , et al . The concept of a cementless isoelastic monoblock cup made of highly cross-linked polyethylene infused with vitamin E: radiological analyses of migration and wear using EBRA and clinical outcomes at mid-term follow-up. BMC Muscoskel Disord. 2021;22(1):107.
    [Google Scholar]
  43. , , , , , . Texture analysis of trabecular bone around RM-Pressfit cementless acetabulum in a series of 46 patients during a 5 year period. J Orthop Traumatol: Surgery and Research. 2019;105(7):1283-1287.
    [Google Scholar]
  44. , , , . Bone preservation in total hip arthroplasty. J Arthroplasty. 2022;37(6):1118-1123.
    [Google Scholar]

Fulltext Views
63

PDF downloads
11
View/Download PDF
Download Citations
BibTeX
RIS
Show Sections

Suggested read for related articles: